1. Field of the Invention
The present invention relates to a structure for transmitting the power of an engine in a motorcycle or the like and, in particular, to the structure in which an intermediate shaft is interposed between a crankshaft and the main input shaft of a transmission. The invention also relates to a process for assembling said structure.
2. Description of Background Art
A structure for transmitting the power of an engine using such an intermediate shaft is already publicly known and, for example, Japanese Examined Patent Publication No. 7-54134 discloses a structure in which an intermediate shaft driven gear and an intermediate shaft driving gear are disposed on an intermediate shaft and in which the intermediate shaft driven gear is engaged with the driving gear of a crankshaft inside a crankcase, and in which the intermediate driving gear is engaged with the input gear of the input shaft of a transmission outside the crankshaft, and in which a balancer weight is integrally formed inside the crankcase of the intermediate shaft.
Further, Japanese Examined Patent Publication No. 7-94859 discloses a power transmission structure in which an idle gear is arranged at the end portion projecting outside the crankcase of an intermediate shaft, and is engaged with both the driving gear of a crankshaft and the input gear of the input shaft of a transmission, which are disposed outside the crankcase.
In this connection, when an intermediate shaft driven gear and a intermediate shaft driving gear are disposed on an intermediate shaft inside and outside the crankcase, as disclosed in Japanese Examined Patent Publication No. 7-54134, many man hours are required for assembly. Thus, it would be desirable to improve workability of assembly. Further, if a balancer weight is mounted on the intermediate shaft inside the crankcase, restrictions are introduced into the layout, depending on the presence or absence of a clearance between the balancer web and a crank web. Therefore, it would be desirable to provide an improved structure capable of increasing the layout flexibility and of producing a greater balancing effect.
Further, if a gear disposed on the intermediate shaft is used only as an idle gear, as Japanese Examined Patent Publication No. 7-94859 discloses, a free speed reduction ratio cannot be obtained and the distance between the intermediate shaft and the input shaft of the transmission is inevitably made greater.
The object of the present invention is to solve these problems.
In order to solve the problem described above, a first element of the present invention comprises a crankshaft, an intermediate shaft, an input shaft of a transmission, and an output shaft of the transmission, wherein these respective shafts are supported by a crankcase, characterized in that an intermediate shaft driven gear and an intermediate shaft driving gear are mounted adjacently in the axial direction on a right end of the intermediate shaft at a location outside the crankcase, and that the intermediate shaft driven gear is engaged with the driving gear of the crankshaft, and that the intermediate shaft driving gear is similarly engaged with an input gear of the input shaft of the transmission, also in a position outside the crankcase.
The present invention is also characterized in that at least one balancer weight is mounted on the left end of the intermediate shaft, which projects outside the crankcase.
In addition, the present invention is characterized in that a sub-gear having the same diameter as the intermediate shaft driven gear is overlaid on the intermediate shaft driven gear, and that a spring for turning both the gears in the opposite direction is disposed between both the gears to form a canceling structure. The intermediate shaft driving gear is also formed in the canceling structure, and has a sub-gear similar to the sub-gear of the intermediate driven gear. All four of these gears are butted together and held in place by a washer and nut, fixing all of these gears in a thrust direction.
In the present invention, the intermediate shaft driven gear and the intermediate shaft driving gear are disposed on the intermediate shaft outside the crankcase. Therefore, it is possible to mount all of the shafts, namely the crankshaft, the intermediate shaft, the main input shaft of the transmission, and the output shaft of the transmission, on the crankcase, and then to easily mount all of the gears for transmitting the power from one of these shafts to another at positions outside the crankcase. This configuration results in improved in workability of assembly of the members involved. Further, since the intermediate shaft driven gear and the intermediate shaft driving gear are mounted on the intermediate shaft in two steps, it is possible to freely set a speed reduction ratio. Moreover, the configuration of this invention shortens the distance between the intermediate shaft and the crankshaft, and the distance between the intermediate shaft and the input shaft of the transmission.
In the present invention, since the balancer weight is disposed on the intermediate shaft at the portion projecting outside the crankcase, unlike conventional embodiments in which the balancer weight is disposed inside the crankcase, the balancer weight can be mounted without regard for the clearance between itself and a crank web, thereby increasing layout flexibility. In addition, since the balancer weight is mounted at the position away from the center of the engine, it is possible to produce a greater effect for regulating lateral vibrations.
In the present invention, each of the intermediate shaft driven gear and the intermediate shaft driving gear is formed in a canceling structure, with each gear having a sub-gear. All four of these gears are then butted together and fixed in the thrust direction by means of a simple washer and nut, eliminating the need for a special fixing structure, and hence simplifying the structure.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.